IMO, the best way to enable students to avoid the easy option of plagiarism is to pose a question that requires personal input using higher order thinking skills and which cannot be answered by copy-and-paste. Jamie McKenzie wrote about this in 1997 - The Question is the Answer http://fno.org/oct97/question.html

More recently, Joy McGregor and Kirsty Williamson have done extensive research and they found that the more a student copied, the better the mark they received. You can read more in
David Loertscher has also addressed the issue in his action research "Ban Those Bird Units" http://books.google.com.au/books/about/Ban_those_bird_units.html?id=sJmsAQAACAAJ <http://books.google.com.au/books/about/Ban_those_bird_units.html?
David Loertscher has also addressed the issue in his action research "Ban Those Bird Units" http://books.google.com.au/books/about/Ban_those_bird_units.html?id=sJmsAQAACAAJ <http://books.google.com.au/books/about/Ban_those_bird_units.html?id=sJmsAQAACAA J&redir_esc=y> &redir_esc=y